Hello Forum,

I have data on prices and I am trying to pull off a difference coefficient. So, I have the mean price for product X for Nov 13, Dec 13, Jan 14 and Feb 14.
I wanted to see the difference between mean prices of 2013 and 2014.

So, in order to get the difference in means I get the price means of Jan 14 and Feb 14 and divided by two and subtract with the means price of Nov 13 and Dec 13 divided by two as well.

I see this in a paper.
However, they also reported standard error of this transformation.

Does anyone know how to get the sd. error?

You help is very much appreciated.
Thank you!

Lena